Audio Masking Effect – Part 3
Temporal difference in sound, peculiarity of the perception of timbre.
The most important characteristic (especially in the context of high-class “hi-fi” acoustics) of the human auditory system is the ability to pick up subtle temporal differences in the structure of the sound signal. The mechanism of this phenomenon is not fully understood, however, it is directly related to the fact that the auditory system is not linear. It is thanks to this that it is practically impossible to “fool” the perception mechanism into the level of the precise recreation of a live sound image and other musical nuances. Even the most modern high-fidelity (hi-fi) sound reproduction systems still do not fully account for this critical human ability to respond to temporal differences in sound. Some trained people (in terms of sounds and music) can pick up the time difference of signals in the range of 2-7 ms. The main significant characteristic of this phenomenon of perception is that
The characteristics of attack and release determine the timbre of the sound of a particular instrument, since the time interval of these periods for most instruments is between 5-360 ms. Compliance with the sequence of triphasic periods (attack, stationary part, decay) is extremely important, as it is this that determines down to the smallest detail how accurately the timbre of each particular musical reproduction will be perceived or transmitted. If the periods are reversed, for example, the period of decay with the period of attack, then the person will not be able to recognize the timbre of the sound. This circumstance allows listening to musical compositions in rooms and other volumes, since the reflected sounds do not have time to influence and mask the signal formation stage, that is, the attack phase, leaving it practically “clean” and intact. In this case, the timbre does not suffer much. A set of tools containing close harmonics in the spectral composition, establishes a certain timbre character to the whole sound as a whole, as if “pulling the lead”. This determines the spectral energy distribution and the area of concentration in the frequency range. This zone of concentration of sound energy tends to change in one direction or another under the influence of certain factors, such as volume.
Very often, with increasing volume, the sound acquires a ringing brightness due to the corresponding shift of the area of concentration and an increase in the influence of the high-frequency segment of the spectrum. During attack-stationary-decay phase transformations, complex processes of dynamic change of the saturation zone take place, depending on which harmonics “saturate” a segment of the range at any particular moment in time. As you know, the timbre of a sound depends on the spectral and temporal components of the signal. However, there is a characteristic circumstance that determines the perception of the timbre. In the upper sections of the human auditory system, there are special neurons, also called “novelty” neurons. These neurons fire only when the stationary signal changes. Using the example of music, we can say that its “turn-on” occurs with “bright” and dynamic changes in tone, volume, sound balance and others. Otherwise, the listener stops perceiving sound information of any nature, be it emotional, informational or aesthetic components.
